#134 add message about actual value when assertion failed

This pull request is for issue: #134

During todays hackaton at @pragmatists we added displaying message about actual value when assertion failed for: `isEqualToComparingFieldByField`, `isEqualToIgnoringGivenFields`, `isEqualToIgnoringNullFields`, `isEqualToComparingOnlyGivenFields`. 

`isEqualToComparingFieldByField` was the subject of the issue. Others (similar cases) were needed to eliminate compilation errors and to make change consistent.

So new message after assertion error will look like this:

`Expecting value <10> in field <"y"> but was <2> in ...`
instead of:
`Expecting value <10> in field <'y'> of ..`

And  

`Expecting values:
  <[9, 11]>
in fields:
  <["x", "z"]>
but were:
  <[1, 3]>
in ...`
instead of:
`Expecting values:
  <[9, 11]>
in fields:
  <['x', 'z']>
of ..`